A tumor suppressor protein with
critical functions in normal cells. A mutation
in the gene that encodes it, p53, can result
in loss of control over cell division and thus
child, + genes, born). Reproduction by
immature or larval animals caused by
acceleration of maturation. Progenesis.
child, + morphe, form). Retention of
ancestral juvenile features in later stages of
the ontogeny of descendants.
An affiliation between an adult
male and an adult female for reproduction.
Characteristic of monogamous species.
(L. mantle). Mantle of a
mollusc or brachiopod.
(Gr. pan, all, + genesis, descent). Darwin's hypothesis that
hereditary characteristics are carried by
individual body cells that produce particles
that collect in the germ cells.
(L. nipple). A small
nipplelike projection. A vascular process
that nourishes the root of a hair, feather, or
(L. pimple). Respiratory
processes on skin of sea stars; also, pustules
(Gr. para, beside, + biosis, mode of life). The fusion of two
individuals, resulting in mutual physiological
beside, + mylos, mill, grinder). Organelles
containing the starch-like substance
paramylon; in some algae and flagellates.
(Gr. para, beside, + phyle, tribe). The condition that a taxon
or other group of organisms contains the
most recent common ancestor of all
members of the group but excludes some
descendants of that ancestor; contrasts with monophyly and polyphyly
beside, + pous, podos, foot). One of the
paired lateral processes on each side of
most segments in polychaete annelids;
variously modified for locomotion,
respiration, or feeding.
from para, beside, + sitos, food). The
condition of an organism living in or on
another organism (host) at whose expense
the parasite is maintained; destructive
(Gr. para, beside, + sympathes, sympathetic,
from syn, with, + pathos, feeling). One of
the subdivisions of the autonomic nervous
system, whose fibers originate in the brain
and in anterior and posterior parts of the
poured in beside). In lower animals, a
spongy mass of vacuolated mesenchyme
cells filling spaces between viscera, muscles,
or epithelia; in some, cell bodies of muscle
cells. Also, the specialized tissue of an
organ as distinguished from the supporting
beside, + enchyma, infusion). Flagellated,
solid-bodied larva of some sponges.
(L. paries, wall).
Something next to, or forming part of, a
wall of a structure.
(Gr. parthenos, virgin, + L. from Gr. genesis,
origin). Unisexual reproduction involving
the production of young by females not
fertilized by males; common in rotifers,
cladocerans, aphids, bees, ants, and wasps.
A parthenogenetic egg may be diploid or
disease, + N.L. genic, giving rise to).
Producing or capable of producing disease.
See polymerase chain reaction
A hierarchy of social privilege in a
flock of birds.
(L. comb). Any of several types of
comblike structures on various organisms,
for example, a pigmented, vascular, and
comblike process that projects into the
vitreous humor from the retina at a point of
entrance of the optic nerve in the eyes of
all birds and many reptiles.
(L. comb, pl. of pecten).
Sensory appendage on abdomens of
(L. pectoralis, from pectus, the breast). Of or pertaining to the
breast or chest; to the pectoral girdle; or to
a pair of horny shields of the plastron of
Asexual reproduction found
in sea anemones, a form of fission.
(L. pedalis, of or
belonging to the foot). Flattened blade at
the base of the tentacles in cubozoan
(L. pediculus, little foot). A
small or short stalk or stem. In insects, the
second segment of an antenna or the waist
of an ant.
little foot, + aria, like or connected with).
One of many minute pincerlike organs on
the surface of certain echinoderms.
(L. pes, pedis, foot, + palpus, stroking, caress). Second pair of
appendages of arachnids.
(L. pedunculus, dim. of pes, foot). A stalk. Also, a band of white
matter joining different parts of the brain.
(Fr. fur). Hairy covering of
(Gr. pelagos, the open sea).
Pertaining to the open ocean.
(L. pellicula, dim. of pellis,
skin). Thin, translucent, secreted envelope
covering many protozoa.
(L. pelvis, a basin). Situated at
or near the pelvis, as applied to girdle,
cavity, fins, and limbs.
(Gr. pelyx, basin, + sauros, lizard). Any of a group of
carnivorous Permian synapsids distinguished
by powerful jaws, stabbing teeth, and a
large skin-covered sail on the back.
(Gr. pente, five, + daktylos, finger). With five digits, or five
fingerlike parts, to the hand or foot.
(Gr. pente, five, + meros, part). A radial
symmetry based on five or multiples thereof.
(Gr. peptein, to digest, + ase, enzyme suffix). An enzyme that
breaks down simple peptides, releasing
A bond that binds amino acids
together into a polypeptide chain, formed
by removing an OH from the carboxyl
group of one amino acid and an H from the amino group of another to form an amide
(L. perennis, throughout the year, + Gr. branchia, gills). Having permanent gills,
relating especially to certain paedomorphic
around, + kardia, heart). Area around
heart; membrane around heart.
around, + ostrakon, shell). Outer horny
layer of a mollusc shell.
(Gr. peripherein, to
move around). Structure or location distant
from center, near outer boundaries.
(Gr. peri, around, + proktos, anus). Region of aboral plates
around the anus of echinoids.
(Gr. peri, around, + sarx, flesh). Sheath covering the stalk
and branches of a hydroid.
odd, + daktylos, finger, toe). Pertaining to
an order of ungulate mammals with an odd
number of digits.
compressing around). The series of
alternate relaxations and contractions that
serve to force food through the alimentary
around, + stoma, mouth). Foremost true
segment of an annelid; it bears the mouth.
stretched around). The membrane that
lines the coelom and covers the coelomic
A transporter molecule; a molecule
in the cell membrane that makes it possible
for another molecule (to which the
membrane is not otherwise permeable) to
be transported across the membrane, that is,
(Gr. petalon, leaf, + eidos, form). Describes flowerlike
arrangement of respiratory podia in irregular
(potential of hydrogen). A symbol referring
to the relative concentration of hydrogen
ions in a solution; pH values are from 0 to
14, and the lower the value, the more acid
or hydrogen ions in the solution. Equal to
the negative logarithm of the hydrogen ion
(Gr. phagein, to eat, + kytos, hollow vessel). Any cell that
engulfs and devours microorganisms or
(Gr. phagein, to
eat, + kytos, hollow vessel). The
engulfment of a particle by a phagocyte or
(Gr. phagein, to eat, + soma, body). Membrane-bound vesicle in
cytoplasm containing food material engulfed
(Gr. phagein, to eat, + trophe, food). A heterotrophic organism
that ingests solid particles for food.
, pl. pharynges (Gr. pharynx, gullet). The part of the digestive
tract between the mouth cavity and the
esophagus that, in vertebrates, is common
to both digestive and respiratory tracts. In
cephalochordates the gill slits open from it.
(Gr. phasma, apparition,
phantom, + id). One of a pair of glands or
sensory structures found in the posterior
end of certain nematodes.
(Gr. phaneros, visible,
evident). Refers to the use of a criterion of
overall similarity to classify organisms into
taxa; contrasts with classifications based
explicitly on a reconstruction of phylogeny.
(Gr. phainein, to
show). The visible or expressed
characteristics of an organism, controlled by
the genotype, but not all genes in the
genotype are expressed.
The hypothesis that
new traits, even those that are strikingly
different from ancestral ones, evolve by a
long series of small, incremental steps.
(Gr. pherein, to carry, + hormon, exciting, stirring up). Chemical
substance released by one organism that
influences the behavior or physiological
processes of another organism.
(phosphate + gen). A
term for creatine phosphate and arginine
phosphate, which store and may be sources
of high-energy phosphate bonds.
(phosphate + ide). A
lipid with phosphorus, such as lecithin. A
complex phosphoric ester lipid, such as
lecithin, found in all cells. Phospholipid.
addition of a phosphate group, that is,
-PO3, to a compound.
(Gr. photos, light, + autos, self, + trophos,
feeder). An organism requiring light as a
source of energy for making organic
nutrients from inorganic raw materials.
light, + synthesis, action or putting
together). The synthesis of carbohydrates
from carbon dioxide and water in
chlorophyll-containing cells exposed to light.
(Gr. phos, light, + taxis, arranging, order). A taxis in
which light is the orienting stimulus. An
involuntary tendency for an organism to
turn toward (positive) or away from
(Gr. phos, photos,
light, + trophe, nourishment). Organisms
capable of using CO2 in the presence of
light as a source of metabolic energy.
A model of evolution in
which morphological evolutionary change is
continuous and incremental and occurs
mainly within unbranched species or lineages over long periods of geological
time; contrasts with punctuated
leaf, + pous, podos, foot). Leaflike
swimming appendage of branchiopod
phylogenetic species concept
(basal) cluster of organisms, diagnosably
distinct from other such clusters, and within
which there is a parental pattern of ancestry
(Gr. phylon, tribe, race, + geneia, origin). The origin and
diversification of any taxon, or the
evolutionary history of its origin and
diversification, usually presented in the form
of a dendrogram.
, pl. phyla (N.L. from Gr. phylon, race, tribe). A chief category,
between kingdom and class, of taxonomic
classifications into which are grouped
organisms of common descent that share a
fundamental pattern of organization.
(L. physiologia, natural science). A
branch of biology dealing with the organic
processes and phenomena of an organism
or any of its parts or of a particular bodily
the class Phytomastigophorea, plantlike
(Gr. phyton, plant, + phagein, to eat). Organisms that feed on
(Gr. pilidion, dim. of pilos, felt cap). Free-swimming, hat-shaped
larva of nemertine worms.
(Gr. pinax, tablet, + kytos, hollow vessel). Flattened cells
composing dermal epithelium in sponges.
plank, tablet, + derma, skin). The layer of
pinacocytes in sponges.
(L. feather, sharp point). The
external ear. Also a feather, wing, or fin or
(Gr. pinein, to drink, + kytos, hollow vessel, + osis, condition). Taking up of fluid by
endocytosis; cell drinking.
(L. flat cake). The
vascular structure, embryonic and maternal,
through which the embryo and fetus are
nourished while in the uterus.
(L. placenta, flat cake, + trophos, one who
feeds). Nutrition of an embryo from a
(Gr. plakos, flat round
plate). Localized, plate-like thickening of
vertebrate head ectoderm from which a
specialized structure develops; such
structures include eye lens, special sense
organs, and certain neurons.
(Gr. plax, plate, + derma, skin). A group of heavily armored
jawed fishes of the Lower Devonian to
(Gr. plax, plakos,
tablet, plate). Type of scale found in
cartilaginous fishes, with basal plate of dentin
embedded in the skin and a backwardpointing
spine tipped with enamel.
(Gr. neuter of planktos,
wandering). The passively floating animal
and plant life of a body of water; compares
(L. planta, sole, + gradus, step, degree). Pertaining to animals
that walk on the whole surface of the foot
(for example, humans and bears); compares
(N.L. dim. from L. planus,
flat). Free-swimming, ciliated larval type of
cnidarians; usually flattened and ovoid, with
an outer layer of ectodermal cells and an
inner mass of endodermal cells.
flat, + Gr. eidos, form). Hypothetical form
representing ancestor of Cnidaria and
(Gr. plasma, a form,
mold). A descendant cell of a B cell,
functions to secrete antibodies.
(Gr. plasma, a
form, mold). A living, external, limiting,
protoplasmic structure that functions to
regulate exchange of nutrients across the
(Gr. plasma, a
form, mold, + lemma, rind, sheath). The
(Gr. plasma, a form,
mold). A small circle of DNA that may be
carried by a bacterium in addition to its
(Gr. plasma, a
form, mold, + eidos, form). Multinucleate
ameboid mass, syncytial.
(Gr. plast, formed, molded, + L. id, feminine stem for particle of
specified kind). A membranous organelle in
plant cells functioning in photosynthesis
and/or nutrient storage, for example,
(Fr. plastron, breast
plate). Ventral body shield of turtles;
structure in corresponding position in
certain arthropods; thin film of gas
retained by epicuticle hairs of aquatic insects.
(Gr. dim. of plattus, flat). A
tiny, incomplete cell in the blood that
releases substances initiating blood clotting.
(Gr. pleion, more, + tropos, to turn). Pertaining to a gene
producing more than one effect; affecting
multiple phenotypic characteristics.
(Gr. plein, to sail, + pous, podos, foot). One of the swimming
appendages on the abdomen of a
condition of a variable character.
(Gr. side, rib). The membrane
that lines each half of the thorax and covers
(L. network, braid). A
network, especially of nerves or blood
, pl. plutei (L. pluteus,
movable shed, reading desk). Echinoid or
ophiuroid larva with elongated processes
like the supports of a desk; originally called
"painter's easel larva".
breathing, + stoma, mouth). The opening
of the mantle cavity (lung) of pulmonate
gastropods to the outside.
(Gr. pous, podos, foot). A
footlike structure, for example, the tube foot
(Gr. poikilos, variable, + thermal). Pertaining to
animals whose body temperature is variable
and fluctuates with that of the environment;
cold blooded; compares with ectothermic
(Gr. polos, axis). In systematics, the
ordering of alternative states of a taxonomic
character from evolutionarily ancestral to
derived conditions. In developmental
biology, the tendency for the axis of an
ovum to orient corresponding to the axis of
the mother. Also, condition of having
opposite poles; differential distribution of
gradation along an axis.
(L. polaris, polar, + Gr. iz,
make). The arrangement of positive
electrical charges on one side of a surface
membrane and negative electrical charges
on the other side (in nerves and muscles).
(from G. S. Poli,
Italian naturalist). Vesicles opening into ring
canal in most asteroids and holothuroids.
(Gr. polys, many, + aner, man). Condition of having more than
one male mate at one time.
(Gr. polys, many, + gamos, marriage). Condition of having more
than one mate at a time.
Inheritance of traits
influenced by multiple alleles; traits show
continuous variation between extremes;
offspring are usually intermediate between
the two parents; also known as blending and quantitative inheritance
(Gr. polys, many, + gyne, woman). Condition of having more
than one female mate at one time.
(Gr. polys, many, + meros, part). A chemical compound
composed of repeated structural units called
polymerase chain reaction (PCR)
technique for preparing large quantities
of DNA from tiny samples, making it
easy to clone a specific gene as long
as part of the sequence of the gene is
process of forming a polymer or polymeric
many, + morphe, form). The presence in a
species of more than one structural type of
(poly + nucleotide): A
nucleotide of many mononucleotides
(Gr. polypous, many-footed).
Individual of the phylum Cnidaria, generally
adapted for attachment to the substratum at
the aboral end, often form colonies.
(Gr. polys, many, + peptein, to digest). A molecule consisting
of many joined amino acids, not as complex
as a protein.
(Gr. polys, many, + phylon, tribe). The condition that a taxon or
other group of organisms does not contain
the most recent common ancestor of all
members of the group, implying that it has
multiple evolutionary origins; such groups
are not valid as formal taxa and are
recognized as such only through error.
Contrasts with monophyly and paraphyly
manifold, + odous, tooth). Having several
sets of teeth in succession.
(L. polypus, polyp). An
individual or zooid in a colony, specifically
in ectoprocts, which has a lophophore,digestive tract, muscles, and nerve centers.
(Gr. polys, many, + ploidy, number of chromosomes). An
organism possessing more than two full
homologous sets of chromosomes.
(Gr. polys, many, + sakcharon, sugar, from
Sanskrit sarkara, gravel, sugar). A
carbohydrate composed of many
monosaccharide units, for example,
glycogen, starch, and cellulose.
(polyribosome) (Gr. polys, many, + soma, body). Two or more ribosomes
connected by a molecule of messenger RNA.
many, + tainia, band). Chromosomes in
the somatic cells of some insects in which
the chromatin replicates repeatedly without
(Gr. polys, many, + zoon, animal). A tapeworm forming a
strobila of several to many proglottids; also,
a colony of many zooids.
(L. Pongo, type genus of
orangutan). Of or relating to the primate
family Pongidae, comprising the anthropoid
apes (gorillas, chimpanzees, gibbons,
(L. populus, people). A group of
organisms of the same species inhabiting a
specific geographical locality.
that new genetic variants become established in a population by increasing
their frequencies across generations
incrementally, initially from one or a few
individuals and eventually characterizing a
majority of the population.
(Gr. porus; passage, pore, + kytos, hollow vessel). Type of cell found
in asconoid sponges through which water
enters the spongocoel.
(L. porta, gate). System of large
veins beginning and ending with a bed of
capillaries; for example, hepatic portal and
renal portal system in vertebrates.
(L. latter). Situated at or toward the
rear of the body; situated toward the back;
in human anatomy the upright posture
makes posterior and dorsal identical.
(Gr. potos, a
drinking, + kytos, hollow vessel).
Endocytosis of certain small molecules and
ions bound to specific receptors limited to
small areas on the cell surface. The areas of
the receptors are invaginated and pinch off
to form tiny vesicles. See caveolae
The possession of a trait that
coincidentally predisposes an organism for
survival in an environment different from
those encountered in its evolutionary history.
The chemical synthesis
that occurred before the emergence of life.
(L. praecoquere, to
ripen beforehand). Referring (especially) to
birds whose young are covered with down
and are able to run about when newly
(L. praedator, a plunderer, praeda, prey).
Living by killing and consuming other
(L. praedator, a
plunderer, praeda, prey). An organism that
preys on other organisms for its food.
(L. prehendere, to
seize). Adapted for grasping.
A resistance to reinfection by an
animal (host) when some infective
organisms remain in the host's body.
primary bilateral symmetry
to a radially symmetrical organism descended
from a bilateral ancestor and developing
from a bilaterally symmetrical larva.
primary radial symmetry
Usually applied to
a radially symmetrical organism that did not
have a bilateral ancestor or larva, in contrast
to a secondarily radial organism.
(L. primus, first). Any
mammal of the order Primates, which
includes the tarsiers, lemurs, marmosets,
monkeys, apes, and humans.
(L. primus, first). Primordial; ancient;
little evolved; said of characteristics closely
approximating those possessed by early
(Gr. pro, before, + boskein, feed). A snout or trunk. Also,
tubular sucking or feeding organ with the
mouth at the end as in planarians, leeches,and insects. Also, the sensory and defensive
organ at the anterior end of certain
(L. producere, to bring forth).
Organisms, such as plants, able to produce
their own food from inorganic substances.
In ecology, the energy
accumulated by an organism that becomes
incorporated into new biomass.
(L. pro, before, + gestare, to carry). Hormone secreted by
the corpus luteum and the placenta;
prepares the uterus for the fertilized egg
and maintains the capacity of the uterus to
hold the embryo and fetus.
(Gr. proglottis, tongue
tip, from pro, before, + glotta, tongue, + id, suffix). Portion of a tapeworm
containing a set of reproductive organs;
usually corresponds to a segment.
(Gr. pro, before, + hormaein, to excite). A precursor of a
hormone, especially a peptide hormone.
procaryotic (Gr. pro, before, + karyon, kernel, nut).
Not having a membrane-bound nucleus or
nuclei. Prokaryotic cells characterize the
bacteria and cyanobacteria.
A region of DNA to which the RNA
polymerase must have access for
transcription of a structural gene to begin.
(Gr. pro, before, + nephros, kidney). Most anterior of three
pairs of embryonic renal organs of
vertebrates, functional only in adult
hagfishes and larval fishes and amphibians,
and vestigial in mammalian embryos. Adj, pronephric
(L. proprius, own, particular, + receptor).
Sensory receptor located deep within the
tissues, especially muscles, tendons, and
joints, that is responsive to changes in
muscle stretch, body position, and
(Gr. pro, before, + L. simia, ape). Any member of a group
of arboreal primates including lemurs,
tarsiers, and lorises, but excluding monkeys,
apes, and humans.
(Gr. pro, before, + soma, body). Anterior part of an
invertebrate in which primitive segmentation
is not visible; fused head and thorax of
(Gr. proso, forward, + pyle, gate). Connections between the
incurrent and radial canals in some sponges.
of fatty-acid hormones, originally discovered
in semen, known to have powerful effects
on smooth muscle, nerves, circulation, and
(Gr. protos, first, + stoma, mouth, + -idion, dim. ending).
Anterior closure of a metameric animal,
anterior to the mouth.
(Gr. protos, first, + aner, male). Condition of hermaphroditic
animals and plants in which male organs
and their products appear before the
corresponding female organs and products,
thus preventing self-fertilization.
(Gr. protein, + ase,
enzyme). An enzyme that digests proteins;
includes proteinases and peptidases.
(Gr. protein, from
proteios, primary). A macromolecule of
carbon, hydrogen, oxygen, and nitrogen
and sometimes sulfur and phosphorus;
composed of chains of amino acids joined
by peptide bonds; present in all cells.
Glands in the prothorax
of insects that secrete the hormone ecdysone.
before, + thrombos, clot). A constituent of
blood plasma that is changed to thrombin
by a catalytic sequence that includes
thromboplastin, calcium, and plasma
globulins; involved in blood clotting.
(Gr. protos, first). A member
of the kingdom Protista, generally considered
to include the protozoa and eukaryotic algae.
(Gr. protos, first, + koilos, hollow). The anterior coelomic
compartment in some deuterostomes,
corresponds to the axocoel in echinoderms.
A mutually beneficial
interaction between organisms in which the
interaction is not physiologically necessary
to the survival of either.
A subatomic particle with a positive
electrical charge and having a mass of 1836
times that of an electron; found in the
nucleus of atoms.
(Gr. protos, first, + nephros, kidney). Primitive
osmoregulatory or excretory organ
consisting of a tubule terminating internally
with flame bulb or solenocyte; the unit of a
flame bulb system.
(Gr. protos, first, + plasma, form). Organized living substance;
cytoplasm and nucleoplasm of the cell.
(Gr. protos, first, + pous, podos,
foot). Basal portion of crustacean
appendage, containing coxa and basis.
(Gr. protos, first, + stoma, mouth). A group of phyla in which
cleavage is determinate, the coelom (in
coelomate forms) is formed by proliferation
of mesodermal bands (schizocoelic
formation), the mesoderm is formed from a
particular blastomere (called 4d), and the
mouth is derived from or near the blastopore.
Includes the Annelida, Arthropoda, Mollusca,
and a number of minor phyla. Compares with Deuterostomia
before, + ventriculum, ventricle). In birds the glandular stomach between the crop and
gizzard. In insects, a muscular dilation of
foregut armed internally with chitinous teeth.
(L. proximus, nearest). Situated
toward or near the point of attachment;
opposite of distal, distant.
(L. proximus, nearest, + causa). The factors that underlie the
functioning of a biological system at a
particular place and time, including those
responsible for metabolic, physiological,
and behavioral functions at the molecular,
cellular, organismal, and population levels.
(Gr. pseudes, false, + koiloma, cavity). A body cavity not lined
with peritoneum and not a part of the
blood or digestive systems, embryonically
derived from the blastocoel.
(Gr. pseudes, false, + podion, small foot, + eidos, form). A temporary cytoplasmic
protrusion extended out from a protozoan
or ameboid cell, and serving for locomotion
or for taking up food.
Strands of DNA spread apart at certain
locations on giant chromosomes of some
flies where that DNA is being transcribed.
(L. pulmo, lung, + aria, suffix denoting connected to).
Relating to or associated with lungs.
A model of
evolution in which morphological
evolutionary change is discontinuous,
being associated primarily with discrete,
geologically instantaneous events of
speciation leading to phylogenetic
branching; morphological evolutionary
stasis characterizes species between
episodes of speciation; contrasts with phyletic gradualism
(L. girl, doll, puppet). Inactive
quiescent stage of the holometabolous
insects. It follows the larval stages and
precedes the adult stage.
(L. purus, pure, + urina,
urine). Organic base with carbon and
nitrogen atoms in two interlocking rings.
The parent substance of adenine, guanine,
and other naturally occurring bases.
(Gr. pyge, rump,
buttocks, + -idion, dim. ending). Posterior
closure of a metameric animal, bearing
(alter. of pyridine,
from Gr. pyr, fire, + id, adj. suffix, + ine).
An organic base composed of a single
ring of carbon and nitrogen atoms; parent
substance of several bases found in